bai tap lon phan tich dinh luong

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CHNG III : CHUN OXI HA KH

BI 1: 0,1 g mu phn tch cha V, Cr, Mn c phn hy thnh dung dch . Sau khi chha dung dch cc nguyn t tn ti di dng VO 2+ , Cr2O72- , MnO4- .Chun dung dch bng dung dch chun Fe2+ 0,1 M ch ht 50 ml . Ion VO 2+to thnh c chun bng dung dch chun KMnO4 0,01M th ht 5ml . Sau thm vo lng mui pitphtphat to phc vi Mn(III) khi chun Mn 2+ bng dung dch KMnO4 trn , th tch tiu tn ln chun ny l 10ml . Tnh hm lng % mi kim loi trong mu ( V=50,49 ; Cr =52 ; Mn=54,94 ). Bit E 0Fe3+/Fe2+ = 0,77V ; E0VO2+/VO2+=1 V ; E0Cr2O72-/ 2Cr3+= 1,36V ;E0MnO4-/Mn2+= 1,51V

BI GII:Tm tt s chun nh sau:

V, Cr, MnCh ha VO2+,, Fe2+

VO2+, Cr3+, Mn2+MnO4

VO2+, Cr3+, Mn2+MnO4

VO2+, Cr3+, Mn3+ Trong mu phn tch cha V, Cr , Mn Sau khi ch ho ta c dung dch gm: VO2 2 , Cr2 O7 , MnO4 . * Chun dung dch bng dung dch tiu chun Fe2+ 0,1M ht 50ml.1 Trn Th M L Lp Ha 3B Bi tp ln2

CHNG III : CHUN OXI HA KH

Ta c:

E o Fe3+ / Fe2+E oVO2+ /VO2+

= 0,771(V) = 1 (V)

E o Cr2O72 / 2Cr3+ E o MnO4 / Mn2+

= 1,33 (V) = 1,51 (V)

Vy th t phn ng chun xy ra l: + u tin Fe2+ kh MnO4 thnh Mn2+: 5 Fe2+ Fe3+ + e Mn2+ + 4H2O 5Fe3+ + Mn2+ + 4H2O (1)

MnO4 + 8H+ + 5e

5Fe2+ + MnO4 + 8H+

+ Sau : Fe2+ kh Cr2 O7 6 Fe2+2

2

thnh Cr3+:

Fe3+ + e 2Cr 3+ + 7H2O 2Cr 3+ +6Fe3+ + 7H2O

Cr2 O7 + 14H+ + 6e6Fe2+ + Cr2 O7 + 14H+ + Cui cng Fe2+ kh VO2 + thnh VO2+: Fe2+ Fe3+ + e2

+ VO2 + 2H+ + e

VO2+ + H2O Fe3+ + VO2+ + H2O

Fe2+ + VO2 + + 2H+ Vy ta c: S lg VO2 + + S lg Cr2 O72

+ S lg MnO4 = S lg Fe2+ (S lg: s ng lng gam) (*) (S: s ng lng gam )

SVO + + S Cr O 2 + S MnO = S 2 + 2 2 7 4 Fe

Gi x, y, z ln lt l s ng lng gam ca V, Cr v Mn trong mu phn tch ban u. Sau khi ch ho ta c dung dch gm: VO2 2 , Cr2 O7 , MnO4 .2 Trn Th M L Lp Ha 3B Bi tp ln2

CHNG III : CHUN OXI HA KH

Ta c :

SVO +2

= SV = x

S Cr O 2 = 3 SCr = 3y 2 7 S MnO = 5 SMn = 5z 4

S Fe2 + =

5.10-3 = 5.10-3 (**)

Thay vo (*) ta c : x + 3y + 5z =

*Sau chun ion VO2+ to thnh bng dung dch chun KMnO4 0,01M ht 5ml. 5 VO2+ + H2O+ VO2 + 2H+ + e

MnO4 + 8H+ + 5e

Mn2+ + 4H2O Mn2+ +5 VO2 + + 2H+ (2)

5VO2+ + H2O + MnO4 Ta c:

SVO 2 + = S MnO = 4

= 2,5.10-4 = x

(***)

* Mt khc qu trnh chun VO2+ bng dung dch chun KMnO4 to ra Mn2+ , vy Mn2+ trong dung dch lc ny c tao ra t phng trnh (1) v (2). + (1) : SMn2+ to ra = SMn ban u = z

+ (2) : SMn2+ to ra =

1S 1 MnO4 chun = 5 5

= 5. 10-5

Vy tng s ng lng ca Mn2+ trong dung dch lc ny l: SMn2+ = z + 5. 10-5

*Chun Mn2+ bng dung dch chun KMnO4 0,01M ht 10ml:3 Trn Th M L Lp Ha 3B Bi tp ln

CHNG III : CHUN OXI HA KH

4

Mn2+

Mn3+ + e MnO4 + 8H+ + 4e

Mn3+ + 4H2O

4Mn2+ + MnO4 + 8H+ Ta c:

4Mn3+ + 4H2O

SMn2+ = S MnO4 Hay : z + 5. 10-5 = = 4.10-4 z = 3,5 .10-4 (****)

T (**) ; (***) ;(****) ta c h sau : x + 3y + 5z = 5.10-3 x = 2,5 . 10-4 z = 3,5 .10-4 y = 10-3

Vy: + SV = x = 2,5.10-4 Khi lng ca V l : mV = SV v = 2,5.10-4 50,94 = 0,0127 (g )

Phn trm ca V l : + SCr = y = 10-3 Khi lng ca Cr l : mCr = SCr Phn trm ca Cr l : + SMn = z = 3,5.10-4 Khi lng ca Mn l : mMn =SMn Phn trm ca Mn l :Mn Cr

12,7 %

= 10-3

= 0,052 (g)

= 52 %

= 3,5.10-4 . 54,94 = 0,0192(g ) ( : ng lng gam )

= 19,2%

4 Trn Th M L Lp Ha 3B Bi tp ln

CHNG III : CHUN OXI HA KH

BI 2: nh phn Fe , Cr ,Ti trong hn hp ngi ta ch ha v thu c 100 mldung dch cha Cr3+ ; Fe3+ ; TiO2+ ( Dung dch A). Ly 20 ml dung dch A cho qua ct kh km v hng dung dch chy ra khi ct vo mt bnh kn c kh quyn khng kh cha oxi .Chun dung dch thu c bng dung dch chun KMnO4 0,02 M th ht 43 ml . Ly 20ml dung dch A na, cho qua ct kh bc , chun dung dch thu c bng dung dch chun K2Cr2O7 0,01M th ht 25,2ml . Ly 20 ml dung dch A thm vo NH3 v H2O2 , un si phn hy ht H2O2 d , lc b kt ta , axt ha nc lc thu c v chun bng dung dch Fe2+ 0,05 M th ht 12,4 ml . Tnh hm lng ( s mg) ca mi kim loi trong dung dich ban u . (Bit Cr =52 ; Fe = 56; Ti = 48 ) .Bit E0TiO2+/Ti3+ = 0,1 V ; E0MnO4-/Mn2+= 1,51V ; E0Cr2O72-/ 2Cr3+= 1,36V ;E0Fe3+/Fe2+ = 0,77V

Fe, Cr, Ti

BI GII: Tm tt s chun nh sau:

Fe3+, Cr3+, TiO2+ Fe3+, Cr3+, TiO2+

Fe2+, Cr2+, Ti3+

Fe2+, Cr3+, TiO2+

Fe3+Cr2O72- TiO2+

5 Trn Th M L Lp Ha 3B Bi tp ln

Fe , Cr , TiO

3+

3+

2+

Fe , Cr , TiO

3+

3+

2+

Fe , Cr3+, TiO2+

3+

CHNG III : CHUN OXI HA KH

Ch ho

Ct kh km

ct kh bc NH3,H2O2

KMnO4 K2Cr2O7Fe2+

*Xt trong 20ml dung dch A:

Ta c:

E o Fe3+ / Fe2+

= 0,771 (V) ; E o Cr 3+ / Cr 2+ = - 0,408 (V)

6 Trn Th M L Lp Ha 3B Bi tp ln

CHNG III : CHUN OXI HA KH

E oTiO2+ /Ti3+

= 0,099 (V) ; E o Zn2+ / Zn = - 0,763 (V)

*Cho 20 ml dung dch A qua ct kh km, khi Cr3+, Fe3+, TiO2+ u b kh:

Vy th t phn ng xy ra: + u tin Zn kh Fe3+ v Fe2+ : Fe2+ Zn Zn + Fe3+ Fe2+ + Zn2+ Fe3+ + e Zn2+ + 2e

+ Sau Zn kh TiO2+ thnh Ti3+ Zn 2 Zn2+ + 2e Ti3+ + H2O

TiO2+ + 2H+ + e

Zn + 2TiO2+ + 4H+

2Ti3+ + Zn2++ 2H2O

+ Cui cng Zn kh Cr3+ thnh Cr2+: Zn 2 Cr3+ +1e Cr2+ Zn + 2Cr3+ 2Cr2+ + Zn2+ Zn2+ + 2e

*Xt trong 20ml dung dch A: Gi s ng lng gam ca Fe3+ ,Cr3+, TiO2+ trong 20ml dung dch A ln lt l x, y, z. Ta c : S Fe2+ = S Fe3+ = x S Cr 2+ = S Cr3+ = y STi 3+ = STiO2 + = z7 Trn Th M L Lp Ha 3B Bi tp ln

CHNG III : CHUN OXI HA KH

Vy dung dch sau khi cho i qua ct kh km l: Fe2+, Cr2+, Ti3+ Chun dung dch thu c bng dung dch chun KMnO4 0,02M ht 43ml. Ta c:

E o MnO4 / Mn2+

= 1,51 (V) nn th t chun l:

+ u tin KMnO4 oxi ho Cr2+ thnh Cr3+ 5 Cr2+ Cr3+ + e Mn2+ + 4H2O

MnO4 + 8H+ + 5e

5Cr2+ + MnO4 + 8H+

5Cr3+ + Mn2+ + 4H2O

+ Sau KMnO4 oxi ho Ti3+ thnh TiO2+: 5 Ti3+ + H2O TiO2+ + 2H+ + e Mn2+ + 4H2O Mn2+ + 5TiO2+ + 2H+

MnO4 + 8H+ + 5e

5Ti3+ + H2O + MnO4

+ Cui cng KMnO4 oxi ho Fe2+ thnh Fe3+: 5 Fe2+ Fe3+ + e Mn2+ + 4H2O

MnO4 + 8H+ + 5e

5Fe2+ + MnO4 + 8H+

5Fe3+ + Mn2+ + 4H2O

Ta c: S Fe2+ + S Cr 2+ + STi 3+ = S KMnO4 x+y+z= Ta c : E0Ag+ / Ag = 0,799 V *Ly 20ml dung dch A cho qua ct kh bc th: Khi ch c Fe3+ b kh to thnh Fe2+: Fe3+ + Ag Fe2+ + Ag+ = 4,3.10-3 ( *)

8 Trn Th M L Lp Ha 3B Bi tp ln

CHNG III : CHUN OXI HA KH

Vy dung dch sau khi cho qua ct kh bc gm : Fe2+ , Cr3+, TiO2+. *Sau chun dung dch thu c bng dung dch chun K2Cr2O7 0,01M ht 25,2 ml. Lc ny K2Cr2O7 ch oxi ho Fe2+ thnh Fe3+:

6

Fe2+

Fe3+ + e2

Cr2O76Fe2+ + Cr2 O72

+ 14H+ + 6e

2Cr3+ + 7H2O

+ 14H+

6Fe3+ +2 Cr3+ + 7H2O

Ta c: S Fe2+ = S Cr2O7 2 Hay x = = 1,512.10-3 (**)

*Ly 20ml dung dch A, thm vo NH3 v H2O2. Khi ch c Cr3+ b oxi ho thnh 2 Cr2O7 . 3 H2O2 2OH- + 2e

2Cr3+ + 14OH- + 6e

Cr2 O7 + 7H2O Cr2 O7 + 7H2O2

2

2Cr3+ + 3H2O2 + 8OH-

(1)2

Vy dung dch sau khi cho thm NH3 v H2O2 gm: Fe3+ , Cr2 O7 Ta c:E0Cr2O72-/ 2Cr3+= 1,36V

, TiO2+

*Chun dung dch thu c bng dung dch tiu chun Fe2+ 0,05M ht 12,4ml. Lc ny ch c Cr2O72

b Fe2+ kh thnh Cr3+ :

6

Fe2+

Fe3+ + e

9 Trn Th M L Lp Ha 3B Bi tp ln

CHNG III : CHUN OXI HA KH

Cr2O7

2

+ 14H+ + 6e2

2Cr3+ + 7H2O + 14H+ 6Fe3+ + 2Cr3+ + 7H2O

6Fe2+ + Cr2 O7

Ta c: V: Cr2 O7 Nn :

S Cr O 2 = S Fe2+ = 2 72

= 6,2 . 10-4 2Cr3+ + 7H2O

+ 14H+ + 6e

S Cr3+ =

1 S Cr2O7 2 62

Nhng t phng trnh (1) ta c c 2mol Cr3+ th to ra 1 mol Cr2 O7 Nn : S Cr3+ = 2. y = 2.

1 S Cr2O7 2 6

Hay

1 .6,2 . 10-4 = 2,0667 .10-4 (***) 6

T (*) ;(**) ;(***) ta c h sau :

x + y + z = 4,3.10-3 x = 1,512.10-3 z = 2,5813.10-3

y = 2,0667 .10-4

Gi mFe , mCr , mTi ln lt l khi lng ca Fe, Cr, Ti trong hn hp phn tch

10 Trn Th M L Lp Ha 3B Bi tp ln

CHNG III : CHUN OXI HA KH

Trong 20ml ta c: S Fe3+ = x = SFe= 1,512.10-3 mFe= SFe =1,512 .10-3 56 = 84,672.10-3 g = 84,672 mg

-4 S Cr 3+ = y = SCr = 2,0667.10

mcr= SCr

= 2,0667.10-4 52 = 10,746.10-3 g = 10,746 mg

STiO2 + = z =STi = 2,5813.10-3 mTi= STi .10-3 48 = 132,902 .10-3 g = 132,902 mg

Vy trong 100ml dung dch A ta c: mFe= 84,672 macr= 10,746 mTi= 132,902 = 423,4 mg = 53,73 mg = 619,51mg

BI 3 : Cho 1g mu lom ( thnh phn H2SO4 , SO3 v SO2 ) vo nc pha thnh 250 ml .Chn 25 ml dung dch ht 21,2 ml NaOH 0,1 M ( chun n pH = 4) . Mc khc , cng chun 100 ml dung dch phn tch trn bng dung dch It ht 37 ml dung dch I2 0,025 N . Tnh thnh phn % cc cu t c trong mu ( Bit H2SO3 c pK1 =1,76 ; pK2 = 7,21 ). BI GII : lum ( H2SO4 ; SO3 ; SO2 ) vo nc pha thnh 250 ml ta c dung dch c cha H2SO4; H2SO3 do: SO3 +H2O SO2 +H2O Ta c : H2SO3 HSO3Nhn xt :11 Trn Th M L Lp Ha 3B Bi tp ln

H2SO4 H2SO3 H+ + HSO3H+ +SO32K1 = 10-1,76 K2 = 10-7,21

CHNG III : CHUN OXI HA KH

pH =

= 4,49

pH =4

Chun n pH = 4 H2SO4 + 2NaOH Na2SO4 + 2H2O H2SO3 + NaOH NaHSO3 + H2O = SO3 = SO2 = Gi x l s gam H2SO4 , y l s gam SO3 , z l s gam SO2 Ta c: S lg H2SO4 + S lg SO3 + S lg SO2 = S lg NaOH

Chun vi I2: SO2 + 2 H2 + I2 SO2 = S lg SO2 = S lg I2 H2SO4 + 2HI

z = 0,148

(2)

x +y +z = 1 (3) Gii phng trnh (1) ,(2) ,(3) ta c x= 0,5254 ; y= 0,3266 ; z = 0,1480

12 Trn Th M L Lp Ha 3B Bi tp ln

CHNG III : CHUN OXI HA KH

Phn trm ca H2SO4 trong lum l :

Phn trm ca SO3 trong lum l :

Phn